Showing papers on "Indentation published in 2003"

Surgical instrument e.g. surgical pliers, clamping tool, cutting tool, has rotation lock that has indentation bar engaging indentation return to fix movable handles of surgical instrument in closed position

Abstract: The instrument (1) has two opposing movable handles (3,4), and a rotation lock for fixing the handles in closed position. The rotation lock includes an indentation bar (14) on one handle (3) and an indentation return (25) on the other handle (4). The indentation bar engages the indentation return to fix the handles in closed position. The indentation bar can be moved in release position through cam motion to open the handles from closed position.

Review of Instrumented Indentation

Abstract: Instrumented indentation, also known as depth-sensing indentation or nanoindentation, is increasingly being used to probe the mechanical response of materials from metals and ceramics to polymeric and biological materials. The additional levels of control, sensitivity, and data acquisition offered by instrumented indentation systems have resulted in numerous advances in materials science, particularly regarding fundamental mechanisms of mechanical behavior at micrometer and even sub-micrometer length scales. Continued improvements of instrumented indentation testing towards absolute quantification of a wide range of material properties and behavior will require advances in instrument calibration, measurement protocols, and analysis tools and techniques. In this paper, an overview of instrumented indentation is given with regard to current instrument technology and analysis methods. Research efforts at the National Institute of Standards and Technology (NIST) aimed at improving the related measurement science are discussed.

Nanomechanical characterisation of solid surfaces and thin films

Abstract: To measure nanomechanical properties of surface layers of bulk materials and thin films, depth-sensing nanoindentation measurement techniques are used commonly. The nanoindentation apparatus continuously monitors the load and the position of the indenter relative to the surface of the specimen (depth of an indent or displacement) during the indentation process. Indentation experiments can be performed at a penetration depth of as low as about 5 nm. This chapter presents an overview of various nanoindentation techniques, various measurement options, and data analysis. Data on elastic-plastic deformation behavior, hardness, elastic modulus, scratch resistance, film-substrate adhesion, residual stresses, time-dependent creep and relaxation properties, fracture toughness, and fatigue are presented.

Measurement of Creep Compliance of Solid Polymers by Nanoindentation

Abstract: Methods to measure the local surface creep compliance of time-dependent materials are proposedand validated in the regime of linear viscoelasticity using nanoindentation. Two different bulkpolymers, Polymethyl Methacrylate (PMMA) and Polycarbonate (PC), were employed in thevalidation study; though it is expected that the methods developed herein can be applied for verysmall amounts of materials and heterogeneous materials. Both Berkovich and sphericalnanoindenters were used to indent into the material in nanoindentation tests. Two loading historieswere used: (1) a ramp loading history, in which the indentation load and displacement wererecorded; and (2) a step loading history, in which the indentation displacement was recorded as afunction of time. Analysis of the linearly viscoelastic material response was performed to measurethe creep compliance functions for the two materials under two different loading histories. The limitof linearly viscoelastic behavior for each of the two materials was determined through theobservation of the indent impression recovery after complete unloading; it is postulated that linearityis achieved if indentation impression is fully recovered after unloading. Results fromnanoindentation tests generally agree well with data from conventional tension and shear tests. It hasthus validated the techniques of measuring linear creep compliance in the glassy state usingnanoindentation with the Berkovich and spherical indenter tips.

Load–displacement behavior during sharp indentation of viscous–elastic–plastic materials

Abstract: A model is developed that describes the sharp indentation behavior of time-dependent materials. The model constitutive equation is constructed from a series of quadratic mechanical elements, with independent viscous (dashpot), elastic (spring), and plastic (slider) responses. Solutions to this equation describe features observed under load-controlled indentation of polymers, including creep, negative unloading tangents, and loading-rate dependence. The model describes a full range of viscous–elastic–plastic responses and includes as bounding behaviors time-independent elastic–plastic indentation (appropriate to metals and ceramics) and time-dependent viscous–elastic indentation (appropriate to elastomers). Experimental indentation traces for a range of olymers with different material properties (elastic modulus, hardness, viscosity) are econvoluted and ranked by calculated time constant. Material properties for these polymers, deconvoluted from single load–unload cycles, are used to predict the indentation load–displacement behavior at loading rates three times slower and faster, as well as the steady-state creep rate under fixed load.

Atomistic simulations of elastic deformation and dislocation nucleation during nanoindentation

Abstract: Nanoindentation experiments have shown that microstructural inhomogeneities across the surface of gold thin films lead to position-dependent nanoindentation behavior [Phys. Rev. B (2002), to be submitted]. The rationale for such behavior was based on the availability of dislocation sources at the grain boundary for initiating plasticity. In order to verify or refute this theory, a computational approach has been pursued. Here, a simulation study of the initial stages of indentation using the embedded atom method (EAM) is presented. First, the principles of the EAM are given, and a comparison is made between atomistic simulations and continuum models for elastic deformation. Then, the mechanism of dislocation nucleation in single crystalline gold is analyzed, and the effects of elastic anisotropy are considered. Finally, a systematic study of the indentation response in the proximity of a high angle, high sigma (low symmetry) grain boundary is presented; indentation behavior is simulated for varying indenter positions relative to the boundary. The results indicate that high angle grain boundaries are a ready source of dislocations in indentation-induced deformation.

The indentation modulus of elastically anisotropic materials for indenters of arbitrary shape

Abstract: The contact of an indenter of arbitrary shape on an elastically anisotropic half space is considered. It is demonstrated in a theorem that the solution of the contact problem is the one that maximizes the load on the indenter for a given indentation depth. The theorem can be used to derive the best approximate solution in the Rayleigh–Ritz sense if the contact area is a priori assumed to have a certain shape. This approach is used to analyze the contact of a sphere and an axisymmetric cone on an anisotropic half space. The contact area is assumed to be elliptical, which is exact for the sphere and an approximation for the cone. It is further shown that the contact area is exactly elliptical even for conical indenters when a limited class of Green's functions is considered. If only the first term of the surface Green's function Fourier expansion is retained in the solution of the axisymmetric contact problem, a simpler solution is obtained, referred to as the equivalent isotropic solution. For most anisotropic materials, the contact stiffness determined using this approach is very close to the value obtained for both conical and spherical indenters by means of the theorem. Therefore, it is suggested that the equivalent isotropic solution provides a quick and efficient estimate for quantities such as the elastic compliance or stiffness of the contact. The “equivalent indentation modulus”, which depends on material and orientation, is computed for sapphire and diamond single crystals.

Correlation between nanoindentation and tensile properties influence of the indentation size effect

Abstract: The nanoindentation test has become one of the most broadly expanded techniques used to measure the mechanical properties in a sub-micron range. However, the interpretation of the data is very difficult due to the Indentation Size Effect (ISE). The ISE can be defined as an increase of the nanohardness by decreasing the indentation depth of the test. In the present work, the ISE of different metals has been studied by performing nanoindentation tests at different imposed depths. Furthermore, tensile tests of these materials have been carried out in order to determine empirical relations between the nanoindentation test results and the tensile properties.

The low velocity impact response of an aluminium honeycomb sandwich structure

Abstract: The low velocity impact response of two aluminium honeycomb sandwich structures has been investigated by conducting drop-weight impact tests using an instrumented falling-weight impact tower. Initially, the rate-sensitivity of the glass fibre reinforced/epoxy skins and aluminium core was investigated through a series of flexure, shear and indentation tests. Here, it was found that the flexural modulus of the composite skins and the shear modulus of the aluminium honeycomb core did not exhibit any strain-rate sensitivity over the conditions investigated here. In addition, it was found that the indentation characteristics of this lightweight sandwich structure can be analysed using a Meyer indentation law, the parameters of which did not exhibit any sensitivity to crosshead displacement rate. The impact response of the aluminium honeycomb sandwich structures was modelled using a simple energy-balance model which accounts for energy absorption in bending, shear and contact effects. Agreement between the energy-balance model and the experimental data was found to be good, particularly at low energies where damage was localised to the core material immediate to the point of impact. The energy balance was also used to identify energy partitioning during the impact event. Here, it was shown that the partition of the incident energy depends strongly on the geometry of the impacting projectile.

Creep indentation of single cells.

Abstract: An apparatus for creep indentation of individual adherent cells was designed, developed, and experimentally validated. The creep cytoindentation apparatus (CCA) can perform stress-controlled experiments and measure the corresponding deformation of single anchorage-dependent cells. The apparatus can resolve forces on the order of 1 nN and cellular deformations on the order of 0.1 micron. Experiments were conducted on bovine articular chondrocytes using loads on the order of 10 nN. The experimentally observed viscoelastic behavior of these cells was modeled using the punch problem and standard linear solid. The punch problem yielded a Young's modulus of 1.11 +/- 0.48 kPa. The standard linear solid model yielded an instantaneous elastic modulus of 8.00 +/- 4.41 kPa, a relaxed modulus of 1.09 +/- 0.54 kPa, an apparent viscosity of 1.50 +/- 0.92 kPa-s, and a time constant of 1.32 +/- 0.65 s. To our knowledge, this is the first time that stress-controlled indentation testing has been applied at the single cell level. This methodology represents a new tool in understanding the mechanical nature of anchorage-dependent cells and mechanotransductional pathways.

A novel ultrasound indentation system for measuring biomechanical properties of in vivo soft tissue.

Abstract: Technologies for soft tissue analysis are advancing at a rapid place For instance, elastography, which provides soft tissue strain images, is starting to be tried in clinical practice as a tool for diagnosing cancer Soft tissue deformation modeling and analysis is also an active area of research that has application in surgery planning and treatment Typically, quantitative soft tissue analysis uses nominal values of soft tissue biomechanical properties However, in practice, soft tissue properties can vary significantly between individuals Hence, for soft tissue methodologies to reach their full potential as patient-specific techniques, there is a need to develop ways to efficiently measure soft tissue mechanical properties in vivo This paper describes a prototype real-time ultrasound (US) indentation test system developed to meet this need The system is based on the integration of a force sensor and an optical tracking system with a commercial US machine integrated with a suite of analysis methodologies In a study on a single-layer phantom, we used the system to compare various methods of estimating linear elastic properties (via a theoretical approximation, 2-D finite element analysis, 3-D finite element analysis and a standard material-testing method) In a second study on a three-layer gelatin phantom, we describe a new finite-element-based inverse solution for recovering the Young's moduli of each layer to show how the system can estimate properties of internal components of soft tissue Finally, we show how the system can be used to derive a modified quasilinear viscoelastic (QVL) model on real breast tissue

Effects of viscoelasticity and time-dependent plasticity on nanoindentation measurements of human cortical bone

Abstract: The viscoelastic and time-dependent plastic effects on the nanoindentation measurement of osteonal lamella in a human cortical bone were investigated. The elastic modulus of osteonal lamella obtained from the quasi-static technique was strongly affected by the indentation rate and time-dependent plasticity. The effects of time-dependent plasticity can be diminished by multiple loading-unloading cycles and a long holding period at maximal load. After minimizing the contribution of time-dependent plasticity to unloading data, it was surprisingly found that the elastic modulus was proportional to indentation strain rate raised to the 0.06 power, which is similar to conventional test results.

Surface damage of soda–lime–silica glasses: indentation scratch behavior

Abstract: Contact mechanics problems are of fundamental interest both to understand the process of surface damage and matter removal in brittle materials, and to develop a method to evaluate their scratch resistance. In order to get insight into these problems in the case of soda–lime–silica glasses, a classical indentation apparatus was used, and an original scratch experimental setup was designed, allowing for a monotonic loading (or unloading) of the indenter combined with a controlled sliding of the specimen beneath the indenter. The influences of the normal load, the moisture level and the glass composition have been studied, and clear relationships were established between the glass compositions and the indentation-scratching behavior. The indentation and scratching characteristics such as the critical-crack-initiation loads and the transition loads between the different scratch regimes were correlated and interpreted in the light of the brittleness index and structural considerations.

In situ electrical characterization of phase transformations in Si during indentation

Abstract: An in situ electrical characterization technique is used to study details of the deformation behavior of crystalline silicon during nanoindentation. The experimental arrangement involves the measurement of current flow through a reverse-biased Schottky diode and exploits a sharp transition from a Schottky to an Ohmic contact that accompanies the formation of a metallic Si-II phase directly under the indenter. This electrical technique is particularly sensitive to the nature and extent of the local Si-I to Si-II phase transformation and allows such changes to be directly correlated with features in nanoindentation load-unload curves, using both spherical and Berkovich indenters. Interestingly, for spherical indentation, the onset of a transformation to a metallic Si-II phase is observed before the so-called "pop-in" event occurs during loading. Furthermore, after the "pop-in" event, fine structure in the electrical behavior suggests that extrusion of the ductile metallic Si-II phase from under the indenter may occur when the transformed area exceeds that of the indenter contact. Indeed, the in situ electrical measurements have provided considerable insight into the evolution of deformation processes during indentation loading and unloading of Si. During unloading, metallic Si-II transforms to less electrically conducting phases of Si. We suggest that, although Si-III and Si-XII are the preferred low pressure phases during pressure release, as diamond anvil studies show, a-Si is often obtained during fast unloading rates as a result of a high kinetic barrier to nucleation of the crystalline phases. Furthermore, we suggest that the pop-out occurs for slow unloading rates as a result of spontaneous nucleation and growth of the crystalline phases at a critical pressure.

Shape memory effect in nanoindentation of nickel–titanium thin films

Abstract: In this study, a series of nanoindentations was made on NiTi shape memory alloy thin films at millinewton loads with a Berkovich indenter. Mapping of the indentation topography using atomic force microscopy reveals direct evidence that the thermally induced martensitic transformation of these films allows for partial indent recovery on the nanoscale. Indeed, recovery is nearly complete at indentation depths of less than 100 nm. A hemispherical cavity model is presented to predict an upper limit to shape memory recovery of sharp indentations.

Hardness trends in micron scale indentation

Abstract: A continuum theory for elastic-plastic solids that accounts for the size-dependence of strain hardening is employed to analyze trends in the indentation hardness test. Strain gradient plasticity theory incorporates an elevation of flow stress when non-uniform plastic deformations occur at the micron scale. Extensive experimental data exists for size-dependence of indentation hardness in the micron range for conical (pyramidal) indenters, and recent data delineates trends for spherical indenters. Deformation induced by rigid conical and spherical indenters is analyzed in two ways: by exploiting an approximation based on spherically symmetric void expansion and by finite element computations. Trends are presented for hardness as a function of the most important variables in the indentation test, including the size of the indent relative to the material length parameters, the strain hardening exponent, the ratio of initial yield stress to Young's modulus, and the geometry of the indenter. The theory rationalizes seemingly different trends for conical and spherical indenters and accurately simulates hardness data presented recently for iridium, a low yield strain/high hardening material. The dominant role of one of the material length parameters is revealed, and it is suggested that the indentation test may the best means of measuring this parameter.

Microscopic superelastic behavior of a nickel-titanium alloy under complex loading conditions

Abstract: The microscopic superelastic behavior of a nickel-titanium (NiTi) alloy has been studied by instrumented indentation experiments using both spherical and pyramidal (e.g., Berkovich) diamond indenters. The indentation load–displacement curves for a superelastic NiTi and an annealed copper were obtained under a range of indentation conditions. We show that indentation-induced superelasticity exists under both spherical and pyramidal indenters, which may be exploited for many applications, ranging from microelectromechanical systems to surface engineering.

Micro-indentation and inverse analysis to characterize elastic /plastic graded materials

Abstract: Properties of actual graded materials were characterized with a new procedure based on inverse analysis This procedure utilizes indirect experimental records obtained from instrumented micro-indentation and extracts key properties of indented specimen through the Kalman filter technique The graded material is composed of mixture of Yittria Partially Stabilized Zirconia (PSZ) and NiCrAlY and it possesses varying elastic � /plastic properties through its thickness This procedure enables determination of the compositional profile and the effective mechanical property without resorting to complex experimental measurements It relies solely on the load � /displacement records of instrumented spherical indentation and the inverse analysis during the post-processing The graded specimens were fabricated by plasma spray deposition process under controlled feeding of PSZ and NiCrAlY powders Prior to testing of the graded materials, single phased coatings were made with each component and analyzed This process allows consistent material constants to be used in the graded material analysis Here PSZ and NiCrAlY were assumed to be elastic and elastic � /plastic, respectively The elastic moduli of both materials were estimated with a common indentation method while the plastic properties of NiCrAlY were determined by modifying the inverse method proposed for the graded materials The latter procedure represents a new indentation method for characterization of homogeneous elastic � /plastic materials Once the properties of constituents were identified, the properties of graded material were estimated with the Kalman filter technique The indented load � /displacement relations simulated from finite element analysis with the estimated properties and that of measured record showed excellent agreement, which assures a high degree of accuracy in the current measurement procedure # 2002 Elsevier Science BV All rights reserved

Indentation testing of human cartilage: sensitivity to articular surface degeneration.

Abstract: Objective To determine, for clinical indentation testing of human articular cartilage, the effects of aging and degeneration on indentation stiffness and traditional indices of cartilage degeneration; the relationship between indentation stiffness and indices of degeneration; and the sensitivity and specificity of indentation stiffness to cartilage degeneration. Methods Osteochondral cores from femoral condyles of cadaveric human donors were harvested. Samples were distributed into experimental groups based on donor age (young [20–39 years], middle [40–59 years], and old [≥60 years]), and a macroscopic articular surface appearance that was either normal or mildly degenerate, without deep erosion. Samples were analyzed for indentation stiffness, cartilage thickness, India ink staining (quantitated as the reflected light score), and Mankin-Shapiro histopathology score. Results Indentation stiffness, India ink staining, and the histopathology score each varied markedly between normal-sample and degenerate-sample groups but varied relatively little between normal samples obtained from different age groups. A decrease in indentation stiffness (softening) correlated with a decrease in the reflectance score and an increase in the overall histopathology score, especially the surface irregularity component of the histopathology score. Receiver operating characteristic analysis suggested that the indentation testing could accurately detect cartilage degeneration as indicated by macroscopic appearance, India ink staining, and histopathology score. Conclusion The indentation stiffness of the normal to mildly degenerate samples tested in this study was sensitive to mild degeneration at the articular surface and was insensitive to changes associated with normal aging or to slight variations in cartilage thickness. This suggests that indentation testing may be a useful clinical tool for the evaluation of early-stage degenerative changes in articular cartilage.

Microstructures of phases in indented silicon: A high resolution characterization

Abstract: This letter investigates the structural changes in monocrystalline silicon caused by microindentation with the aid of the high-resolution transmission electron microscopy. It shows that the transformation zone is amorphous when the maximum indentation load, P-max, is low, but a crystalline phase of high-pressure R8/BC8 can appear when P-max increases. The nanodeformation of the pristine silicon outside the transformation zone proceeds with the mechanical bending and distortion of the crystalline planes. Certain extent of plastic deformation took place due to dislocation slipping. The results seem to indicate that the shear stress component played an important role in the deformation of the transformation zone. (C) 2003 American Institute of Physics.

Limits to the strength of super- and ultrahard nanocomposite coatings

Abstract: Hertzian analysis of the nonlinear elastic response upon unloading provides analytical solutions that were used to verify if the hardness values measured on the super- and ultrahard coatings are self-consistent. The analytical solutions were also used to estimate the tensile strength of the coatings. The highest tensile stress occurs at the periphery of the contact between the coating and the indenter and, in the case of ultrahard coatings, it can reach values in the range of tens of Gpa, thus giving an estimate of their tensile strength. The results show that the tensile strength of the superhard nanocomposites reaches an appreciable fraction of the ideal cohesive strength that is predicted on the basis of the universal binding energy relation. The data are compared with finite element computer modeling in order to obtain a deeper insight into the complex problems. Reliable values of the hardness can be obtained if coatings of a thickness greater than 8 μm are used and the load-independent values are measured at sufficiently large indentation depths of greater than 0.3 μm.

Nanoscale mechanical behavior of individual semiconducting nanobelts

Abstract: Nanobelts are a group of materials that have a rectangle-like cross section with typical widths of several hundred nanometers, width-to-thickness ratios of 5–10, and lengths of hundreds of micrometers. In this letter, nanoindentations were made in individual ZnO and SnO2 nanobelts by a cube corner diamond indenter. It is shown that the effect of indentation size is still obvious for indentation depths less than 50 nm. It is also demonstrated that nanomachining of nanobelts is possible using an atomic force microscope tip.